This page is an attempt to list all those tags that are sensitive to reversal of way direction. When the tags listed here are present on a way, care must to be taken when reversing the direction of that way.

All ways in OpenStreetMap have a direction associated with them because they are represented as an ordered sequence of nodes. Relations have been ordered collections of other objects since API 0.6, and because they may contain ways (which are themselves ordered), they too can be sensitive to reversal of ways within them.

Only ways used to define linear features and that have specific tags have a significant direction, such "one-way" highways or railways, rivers (for their natural flowing direction).

Also some tags added on these ways may have :left, :right, :forward, or :backward sub-keys to restrict their semantic according to the direction of ways.

Ways (even those that are not tagged themselves) may also be used as members of relations with similar forward or backward roles whose interpretation depends on their direction.

Almost all other ways that are only used as outer (or inner) boundaries of areas have a non-significant direction, except (for technical reasons) those that are defining coastlines, because coastlines are extremely long around continents: coastlines must still be drawn in a counter-clockwise direction so that the inner land is on the left, and the outer sea is on the right).

Way direction can be seen on the rendered map if a street has the oneway=yes tag, in Potlatch by a small arrows in the way, in JOSM with an arrow-head on each segment, and in Osm2go with segment arrows which are visible when a way is selected. Forward & backward, left & right has details about the visualization of way direction in editors.